Convoy S21A: SST20 vs SFT40, which will produce more heat?

I’m looking at picking up an S21A with a smaller die LED for throw. I saw this nice BLF review by Mocarny which talks about the uncomfortable temps reached by the S21A with SFT40 onboard. I am wondering if the SST20 would stay cooler? I would prefer to have 5000k or 4000k tint from the SST20 emitter anyway.

I don't know--it depends on the driver configuration. With the same driver, the SFT40 is more efficient. If you're trying to optimize throw then the SFT40 is definitely the better choice, being domeless and more efficient. SST20 in any CCT should be obsolete by now.

If it wasn’t for the CCT options I wouldn’t even consider the SST20.

Are both LEDs driven with the same amount of power in the S21A? I was speculating that the SFT40 version might be driven harder making the comparison of generated heat less cut and dry.

EDIT: Sorry, I realized you said you weren’t sure about the driver configurations. I’ll just leave this comment in case someone else knows.

The SFT40 will be more efficient.

How much throw would you like. One of mine got the flat white 2mm in it, but I dont like it. Like the sst40 best. For more throw a larger reflector would be much better.

Looking at the store descriptions, it seems that the SST20 comes with 3A driver, while SFT40 comes with 6A. So the SFT40 would heat up a bit more, but will also demolish the SST20 version in both output and throw performance.

I would go with the SFT40 version because if you really want low heat, the 35% mode offers comparable performance to the SST20 version at full power, but with way less heat (less current AND more efficiency). SFT40 just gives you the additional option to go full sicko mode.

Oh wow. I don’t know how I missed that about the 3A vs 6A driver. For some reason I was thinking both emitters were on the same listing with only one current listed. Your analysis makes sense. Boy I wish the SFT40 came in 5000k!

I have plenty of floody pocket lights. I thought it would be nice to have a dedicated thrower in a tube shape to make it a true pocket light. The M21F or M21E would outperform the S21A I have no doubt, but neither would be as nice to have in a jeans pocket.

S21a with SFT40 is an awesome light

Heat is a difficult thing.

More amps will generally mean more heat. But you might get a lot more throw and or lumens. So efficiency might be better. But these are not really the same point.

If you want throw may I suggest an Emisar D1 mini. Very pocket friendly and more likely to handle a bit more heat than a true tube light.

Stf-40 will make lots of lumens and lots of throw. Maybe up to 100,00cd in the mini. An SST-20 would be more like 49,000cd and 1000 lumens.

But you can get much nicer tints with the SST-20.

Someone said it should be obsolete, which I think is somewhat harsh.

I don’t have an S21a but I recently got a W1 S2+. It gets way too hot in high IMO.

I suspect an SST-20 driven more moderately would make for a nicer light overall with way better tint if you go 4000k 90+ CRI.

It might happen but it’s a pretty low priority for them. Covid messed up everything and their facilities made some big production shifts over the last couple years. I contacted them some months back and they do indeed have some interest in different temperature options for the SFT40, and they might actually also produce the SFT20 in white (currently it’s only available in colors). If they do that SFT20 it’ll be interesting to see how it compares to other small throwy flat emitters. I’d love a 5K SFT40 as well as long as they can do a decent bin. And assuming light manufacturers can be coaxed into buying reels and putting them in products (or if Digikey, Mouser, etc. will still set cut tape quantities for a decent price).

5000k sst20 can burn by 5a driver but the 4000k works good on 5a driver 3000k can drive by a 6a driver i dont know if it will last…cct can affect the tolerance of the led